varying the composition. It is named
after William Wood (1671–1730).
Woodward, Robert Burns
(1917–79) US organic chemist who
worked at Harvard. He is remembered for his work in organic synthesis, producing many organic
compounds including quinine, cholesterol, cortisone, lysergic acid,
strychnine, chlorophyll, and vitamin
B 12 . In 1965 he formulated the Woodward–Hoffmann rules for certain
types of addition reactions. Woodward was awarded the 1965 Nobel
Prize for chemistry.
Woodward–Hoffmann rules
Rules governing the formation of
products during certain types of organic concerted reactions. The theory
of such reactions was put forward in
1969 by Woodward and Roald Hoffmann (1937– ), and is concerned
with the way that orbitals of the reactants change continuously into orbitals of the products during reaction
and with conservation of orbital symmetry during this process. It is sometimes known as frontier-orbital
theory.
work function A quantity that
determines the extent to which
thermionic or photoelectric emission
will occur according to the Richardson equation or Einstein’s photoelectric equation. It is sometimes
expressed as a potential difference
(symbol φ) in volts and sometimes as
the energy required to remove an
electron (symbol W) in electronvolts
or joules. The former has been called
the work function potential and the
latter the work function energy.
work hardening An increase in
the hardness of metals as a result of
working them cold. It causes a permanent distortion of the crystal
structure and is particularly apparent
with iron, copper, aluminium, etc.,
whereas with lead and zinc it does
not occur as these metals are capable
of recrystallizing at room temperature.
wrought iron A highly reÜned
form of iron containing 1–3% of slag
(mostly iron silicate), which is evenly
distributed throughout the material
in threads and Übres so that the product has a Übrous structure quite dissimilar to that of crystalline cast iron.
Wrought iron rusts less readily than
other forms of metallic iron and it
welds and works more easily. It is
used for chains, hooks, tubes, etc.
wurtzite structure A type of ionic
crystal structure in which the anions
have a hexagonal close packed
arrangement with the cations occupying one type of tetrahedral hole.
Each type of ion has a coordination
number of 4. Examples of this structure are found in ZnS, ZnO, AlN, SiC,
and NH 4 F.
A
• An interactive version of the structure
Wurtz reaction A reaction to prepare alkanes by reacting a
haloalkane with sodium:
2RX + 2Na → 2NaX + RR
The haloalkane is reÛuxed with
sodium in dry ether. The method is
named after the French chemist
Charles-Adolphe Wurtz (1817–84).
The analogous reaction using a
haloalkane and a haloarene, for example:
C 6 H 5 Cl + CH 3 Cl + 2Na → 2NaCl +
C 6 H 5 CH 3
is called the Fittig reaction after the
German chemist Rudolph Fittig
(1835–1910).
Woodward, Robert Burns
558
w
www.AzShimi.ir www.AzShimi.com
after William Wood (1671–1730).
Woodward, Robert Burns
(1917–79) US organic chemist who
worked at Harvard. He is remembered for his work in organic synthesis, producing many organic
compounds including quinine, cholesterol, cortisone, lysergic acid,
strychnine, chlorophyll, and vitamin
B 12 . In 1965 he formulated the Woodward–Hoffmann rules for certain
types of addition reactions. Woodward was awarded the 1965 Nobel
Prize for chemistry.
Woodward–Hoffmann rules
Rules governing the formation of
products during certain types of organic concerted reactions. The theory
of such reactions was put forward in
1969 by Woodward and Roald Hoffmann (1937– ), and is concerned
with the way that orbitals of the reactants change continuously into orbitals of the products during reaction
and with conservation of orbital symmetry during this process. It is sometimes known as frontier-orbital
theory.
work function A quantity that
determines the extent to which
thermionic or photoelectric emission
will occur according to the Richardson equation or Einstein’s photoelectric equation. It is sometimes
expressed as a potential difference
(symbol φ) in volts and sometimes as
the energy required to remove an
electron (symbol W) in electronvolts
or joules. The former has been called
the work function potential and the
latter the work function energy.
work hardening An increase in
the hardness of metals as a result of
working them cold. It causes a permanent distortion of the crystal
structure and is particularly apparent
with iron, copper, aluminium, etc.,
whereas with lead and zinc it does
not occur as these metals are capable
of recrystallizing at room temperature.
wrought iron A highly reÜned
form of iron containing 1–3% of slag
(mostly iron silicate), which is evenly
distributed throughout the material
in threads and Übres so that the product has a Übrous structure quite dissimilar to that of crystalline cast iron.
Wrought iron rusts less readily than
other forms of metallic iron and it
welds and works more easily. It is
used for chains, hooks, tubes, etc.
wurtzite structure A type of ionic
crystal structure in which the anions
have a hexagonal close packed
arrangement with the cations occupying one type of tetrahedral hole.
Each type of ion has a coordination
number of 4. Examples of this structure are found in ZnS, ZnO, AlN, SiC,
and NH 4 F.
A
• An interactive version of the structure
Wurtz reaction A reaction to prepare alkanes by reacting a
haloalkane with sodium:
2RX + 2Na → 2NaX + RR
The haloalkane is reÛuxed with
sodium in dry ether. The method is
named after the French chemist
Charles-Adolphe Wurtz (1817–84).
The analogous reaction using a
haloalkane and a haloarene, for example:
C 6 H 5 Cl + CH 3 Cl + 2Na → 2NaCl +
C 6 H 5 CH 3
is called the Fittig reaction after the
German chemist Rudolph Fittig
(1835–1910).
Woodward, Robert Burns
558
w
www.AzShimi.ir www.AzShimi.com